On refrigeration systems, where the line temperature is lower than the ambient temperature, condensation forms when water vapour comes into contact with colder surfaces of the pipework and equipment.
Eventually, condensation results in considerable damage and there may be further maintenance costs resulting from wet ceilings, spoilt goods or disruption to production processes. The insulation effect of a material also deteriorates greatly when it becomes damp, which can result in large increases in energy use.
At a given temperature and with a given relative humidity, the air contains a defined amount of water vapour. If air is cooled down, it reaches this 100% saturation at a specific temperature. If it is cooled further, some of the water can no longer be held in the form of invisible water vapour and begins to form liquid droplets. Warm air is able to absorb more water vapour than cold air, and so air that is cooled below the dew point results in the formation of moisture on pipes and equipment.
The respective water vapour content of air at a given temperature can be calculated to work out the extent to which air of a certain relative humidity can cool without condensation forming. Applying this to refrigeration applications means that the insulation thickness must be designed so the temperature never falls lower than the dew point anywhere on the surface of the insulation material.
In order to prevent condensation, the surface temperature of the insulation must be as high as or higher than the dew point temperature under defined ambient conditions. This involves knowing the line temperature and the ambient conditions – the ambient temperature and relative humidity – defined as expected maximum values. In addition, it is necessary to determine the thermal conductivity of the insulation material, the object being insulated – the pipe, duct and equipment – and the heat transfer coefficient of the insulation’s surface.
Preventing condensation on the surface of pipework and equipment is a vital requirement in all refrigeration systems where the line temperature is lower than the ambient temperature.
To achieve this, low-temperature insulation must be correctly specified and be able to perform over the long term, even under critical conditions. A key element of this is ensuring that the correct insulation thickness has been used. Another crucial factor is the quality of both the material and the installation, since this has a dramatic effect on performance.
For cold applications, insulation requirements should always be assessed, specified and installed in a way that takes into account all these factors. If unsuitable materials, inadequate insulation thicknesses or poor installation practices are used, the refrigeration system becomes vulnerable to condensation and corrosion.
It is worth remembering that the minimum insulation thicknesses to prevent condensation are different to insulation designed to prevent energy losses. As the results of a recent study show, much higher energy and carbon dioxide savings are possible if greater insulation thicknesses are specified.
It may require a slightly higher investment, but the payback can be substantial if the savings are projected over the whole lifetime of a system.
Michaela Störkmann is technical department manager for EMEA at Armacell